Los nuevos enfoques de la didáctica moderna.

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(C) TYPE OF STUDY:

Case control hospital-based study.

(D) SUBJECTS:

(i) ETHICAL APPROVAL:

Clearance was obtained from the ethical committee of the University of Nigeria Teaching Hospital, Enugu.

(ii) RECRUITMENT:

The study was based on patients aged 12 years and above, with suspected rheumatic heart disease attending the cardiac clinics at the University of Nigeria Teaching Hospital, Enugu.

(iii) INCLUSION CRITERIA:

Fifty-five patients (of both sexes), aged 12 years and above with suspected rheumatic heart disease who were willing to participate in the study were enlisted. They were enrolled with informed consent obtained orally after explaining the objective of the study to them, and /or their accompanying first degree relatives in case of minors. (See Appendix III).

(iv) EXCLUSION CRITERIA:

This included cases of congenital heart disease, hypertensive heart disease, endomyocardial fibrosis, degenerative heart

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disease and uncooperative patients.

(v) SAMPLE SIZE:

This was based on the World Health Organization formula for sample

size determination in a finite population.¹¹⁵ This formula states:

n = Z² p (1- P ) d²

Where n = the minimum required sample size.

Z = Standard deviation value at 95% Confidence Interval (C.I.)

P = a rough approximation to the proportion of the variable in the population. (prevalence)

d = the absolute sampling error that can be tolerated.

For this study,

Z = was taken as 1.96

P =13.3% for prevalence of rheumatic heart disease.

d =5%

And, therefore, the value of n arrived at = 22.77

A total, beyond the calculated sample size, of fifty five (55) patients with rheumatic heart disease who met the inclusion criteria were recruited.

(E) STUDY DESIGN:

(i) History was taken from the patients, after which a clinical

examination was done to establish the diagnosis of chronic rheumatic

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mitral valve disease. The clinical diagnosis was based on the

presence of murmurs of mitral stenosis or mitral incompetence in the absence of obvious causes of mitral incompetence such as: infective endocarditis, ischaemic or traumatic papillary muscle rupture,

degenerative chordal rupture, mitral valve prolapse, mitral annular calcification, parachute mitral valve and atrioventricular septal defect.

(ii) Age, sex, weight, height and blood pressure were recorded.

(iii) Routine Chest X-ray and Electrocardiography were done for the patients. Cardiothoracic ratio was measured from the Chest X-ray.

Cardiothoracic ratio greater than 0.5 (50%) was considered as

cardiomegaly. Left atrial enlargement on ECG was determined using a biphasic p wave with the terminal force in V1 > 1mm.¹¹⁶ Left

ventricular hypertrophy was determined using, SV2 + RV6 >4.0 mV (male); >3.5mV (females).¹¹⁷ Patients were also assessed for various forms of arrhythmias.

(iv) Controls: On enrolment of the chronic rheumatic mitral valve disease patients, suitable controls were identified. These were similar to the cases in age and sex, except that they were not rheumatic heart disease patients. Controls were voluntary subjects recruited from hospital staff and medical students. History and

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physical examination in controls and cases were compared.

Echocardiographic examination was carried out after explanation of the procedure to the patient.

(F) APPARATUS:

ECHOCARDIOGRAPHIC EQUIPMENT: The machine used for

the study was Sono 2000 Hewlett Packard echocardiograph. It has facilities for M-mode, Two-dimensional, Pulsed-wave Doppler,

Continuous wave Doppler and Colour flow Doppler echocardiography.

It also has facilities for simultaneous electrocardiographic display used in timing cardiac events, a video recorder which can also play back either at normal speed or in slow motion, and a video print-out which produces hard copies of the pictures on paper.

The study was done with a 3.7 MHZ transducer. It was used to produce M-mode, two-dimensional, pulsed and continuous wave Doppler

echocardiographic images, either separately or in combinations.

(G) ASSESSMENTS / MEASUREMENTS:

(i) Physical - Age, sex, weight, height, pulse, and blood pressure recordings were done.

(ii) Echocardiographic variables - Examination

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Echocardiographic examination was done with the patient lying down on an examination couch, in a left lateral decubitus position, about 60^o to the horizontal plane.

M-mode examinations were done with the transducer in the usual

echocardiographic window, between the second and fifth intercostal spaces, and within 3 to 4 cm to the left of the left sternal border. M-mode cursor was placed under two-dimensional echocardiographic guidance.¹⁰⁷ The mitral

valve leaflets were assessed for thickening, reduced motility, commissural fusion, calcifications and anterior movement of posterior mitral valve leaflet. Mitral valve c

lesions were classified as purely regurgitant, purely stenotic, or mixed according to recognized echocardiographic criteria. Mitral regurgitation was considered to be pure when associated with unrestricted valve leaflet excursion and a normal mitral valve area as assessed by two-dimensional echocardiography. The left atrium was divided into four levels, starting from a level of 1cm from the MV where mitral regurgitation was

regarded as grade 1, to a level at the top of LA , where rgurgitation was regarded as grade 4. Regurgitation up to the middle of LA is regarded as grade 2, while

regurgitation beyond the middle of LA but not up to the roof is regarded as grade 3. Pure mitral stenosis was diagnosed when no

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echocardiographic evidence of regurgitation was found. MVA of 2-4cm² was regarded as mild, 1-2cm² was regarded as moderate and MVA < 1cm² was severe.

Mixed mitral valve disease was diagnosed when features of both

stenosis and regurgitation were present. Other cardiac valves were also assessed.

All M-mode measurements were made according to the recommendations of the American Society of Echocardiography.¹¹⁸

Two-dimensional echocardiography examinations were done with the transducer in the parasternal echocardiographic window, between the second and fifth intercostal spaces, and within 3 to 4 cm to the left of the left sternal

border for the parasternal long axis and short axis views. The transducer was placed at the apex for the apical- four chamber view. Features of rheumatic mitral valve disease such as calcifications, diastolic doming and restricted movement of anterior mitral leaflet were noted. Mitral valve area was also determined by planimetry via the parasternal short axis view.

The Pulsed wave, continuous wave and colour flow Doppler (transmitral) examinations were done with the transducer at /or slightly to the

left of the apical impulse. The apical four chamber view, optimized to visualize the left ventricular cavity and the maximal excursion of mitral valve leaflets was used.

The cursor was positioned through a plane traversing the left ventricle from apex to mitral valve annulus, with care taken in obtaining

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the smallest possible angle between the direction of diastolic blood flow and orientation of the ultrasonic beam.

All the measurements were done with the picture frozen on the sceen and with the in-built calipers of the echocardiographic equipment. The mean

of measurements from 5 consecutive cycles were taken from each of these indices.

(1) M-mode Echocardiographic measurements:

The following M-mode echocardiographic parameters were measured:

- E- F Slope:

Using two-dimensional echocardiographic guidance, the M-mode cursor was placed perpendicular to the tip of the mitral valve, and the M-mode tracing was obtained. The slope of the E-F was then traced by

the machine’s in-built calipers and the slope was calculated automatically.

- E-point septal separation (EPSS):

With the same view as in E-F slope, the vertical distance between the E-point of the mitral valve M-mode and the interventricular septum was measured. This represents E-point septal separation.

- Left Atrial Dimensions:

Two dimensional parasternal long axis view of the heart was obtained.

The M-mode cursor was then placed at the level of aortic valve leaflets perpendicular to the aortic root in order to obtain an M-mode of the

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aorta and left atrium. The left atrium was measured at its maximum dimension, at the onset of QRS complex, from the leading edge of the posterior wall of the aorta to the dominant line representing the

posterior wall of the left atrium.

- Left Ventricular Septal Wall Thickness at End-Diastole:

A long axis parasternal view was obtained on two-dimensional

echocardiogram. The M-mode cursor was then placed between the mitral valve and the papillary muscle, perpendicular to the

interventricular septum. The M-mode picture obtained from this was used to measure the ventricular septal wall thickness, at the onset of QRS complex from the leading edge of the right septal echoes to the leading edge of the left septal echoes.

- Left ventricular posterior wall thickness at end-diastole:

This was measured at the onset of QRS complex, from the leading edge of the posterior left ventricular echoes, to the leading edge of the epicardial echoes, using the same frozen picture obtained for

ventricular septal wall measurement.

- Left Ventricular End-Systolic Dimension:

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This was measured from the peak of downward motion of the septal

endocardium, to the leading edge of the posterior wall endocardial echoes, using the same frozen picture obtained for the septal wall measurement.

- Left Ventricular End-Diastolic Dimension:

This was measured at the onset of QRS complex, from the leading edge of the left side of the septal endocardium to the leading edge of the posterior wall endocardial echoes, using the same frozen picture obtained for ventricular septal wall measurement.

- Fractional shortening (FS) of the left ventricle (%):

Fractional shortening of the left ventricle was calculated automatically by the echocardiographic equipment using the formula:

FS(%)= LVEDd-LVEDs x 100⁸⁰ LVEDd 1

Where: LVEDd = Left ventricular End-Diastolic Dimension LVEDs = Left ventricular End-Systolic Dimension

(2) Two-Dimensional Echocardiographic measurements:

- Left Ventricular End-Diastolic Volume:

This was measured from apical four-chamber view of a two-

dimensional echocardiography, frozen at the maximum expansion of

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the left ventricular cavity. The in-built calipers of the

echocardiographic equipment were used to trace out the inner edge of the left ventricular cavity, and to obtain its longest axis. The

equipment then calculated the left ventricular end-diastolic volume automatically using Simpson’s rule.⁸⁰

Simpson’s Rule Method:

LV volume =(n-1) At + AnT + Tn3 2 6 where: LV = Left ventricle

n = number of sections A = short axis view area T = thickness of each section.

- Left Ventricular End-Systolic Volume:

This was obtained using the same procedure as for the end-diastolic volume but the frozen picture at the maximum contraction of the left ventricular cavity.

- Left Ventricular Stroke Volume (SV):

The echocardiograhic equipment calculated the ventricular stroke volume automatically using the formula:

SV = LVEDV – LVESV

Where: LVEDV = Left ventricular end-diastolic volume.

LVESV = Left ventricular end-systolic volume.

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- Left Ventricular Ejection fraction (%):

This was calculated automatically by the echocardiographic equipment using the formula:

E.F. = LVEDV- LVESV x 100

LVEDV

- Right atrial volume:

This was estimated using the same technique as for the left ventricular volumes.

- Left atrial volume:

This was estimated using the same technique as for the left ventricular volumes.

- Mitral valve area: This was measured using planimetry.

(3) Doppler Echocardiographic measurements:

- Mitral Pressure Half Time:

This is the time needed for the maximum pressure gradient to decrease by one-half. It was calculated from Doppler signal mitral flow using either the velocity half time (V ½) or base time.

- V max of trans-mitral Doppler:

This is the peak velocity of flow through the mitral valve in early

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diastole which indirectly represents the pressure difference between the left ventricle and left atrium.

-Pressure gradient:

This is the pressure difference between the left ventricle and left atrium.

(H) STATISTICAL ANALYSIS

Data analysis was y computer using SPSS 11.0¹¹⁹ statistical software. Data storage was also by SPSS.

Data are expressed as mean (standard deviation).

Independent t-test for equality of means was used to determine

differences between the means of various groups. Chi square analysis was used to assess relationship between the mitral valve lesions and gender. Pearsons product moment was used to determine the

correlation between some echocardiographic indices and severity of both MI and MS.

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FIGURE 1: Two dimensional echocardiogram showing the apical 4- . Chamber view of the heart with normal cardiac chambers.

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FIGURE 2: Two-dimensional echocardiogram showing parasternal long axis of thickened mitral and aortic valve leaflets

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FIGURE 3: M-mode echocardiogram showing left atrial enlargement in a patient with mitral stenosis

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FIGURE 4: M-mode echocardiogram showing mitral stenosis.

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FUGURE 5: Parasternal short axis showing mitral valve area by planimetry.

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FIGURE 6: Pulsed waved Doppler of mitral regurgitation with aliasing.

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FIGURE 7: Colour flow Doppler showing grade 3 mitral regurgitation.

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FIGURE 8: Continuous wave Doppler showing mitral pressure half time.

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FIGURE 9: Two-dimensional echocardiogram showing measurement of normal left atrium by Simpson’s planimetry.

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Figure 10: Two-dimensional echocardiogram showing dilated left atrium by Simpson’s planimetry.

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FIGURE 11: Electrocardiogram showing left atrial enlargement and left ventricular hypertrophy.

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FIGURE 12: Chest X-ray of mitral valve disease showing cardiomegaly.

In document Innovación didáctica como experiencia educativa para el mejoramiento de la calidad de la educación en la escuela “Ambato” del Cantón Calvas Provincia de Loja durante el periodo 2008-2009 (página 38-42)